Скачать или смотреть Daylight Autonomy: Lightshelf versus Manual/Automated Blinds

A comprehensive daylight simulation study was undertaken for two different façades in tropical Singapore to assess the annual indoor daylight autonomy. While both façades have an external horizontal overhang, the West façade was also designed with a 2.5-meter deep light shelf that
doubles up as an effective shade to protect against the low-angle sun. For the East façade, the glare control is provided by roller blinds. Two different operational modes of the roller blinds were analyzed, namely manual control and automatic control.

The automatic blinds are controlled as prescribed in the IES LM-83-12 guideline used by the LEED and WELL standards. The threshold of activating the blind is when 2% of the work plane area is exposed to 1000 lux or more of direct sunlight between 8:00 – 18:00. When exceeding the threshold, the blind is engaged, otherwise, it remains retracted. For automated blinds the adjustment is instant. For manually adjusted blinds, the frequency of adjustment depends entirely on the users. The following three manual blinds retraction modes were simulated: Daily (blind is retracted every night), weekly (blind is retracted after 1 week), and monthly (blind is retracted after 1 month).

Interestingly, the simulations show a very different effect on the daylight autonomy of the west and east facades. The deep light shelves shade the West facade so effectively that the blinds do not have to be engaged. Therefore, the daylight autonomy remains unchanged along the West façade regardless of the blinds control. For the East façade, however, a significant drop in the daylight autonomy occurs once the blinds control switch from automatic to manual. The simulations show that manually blinds controlled weekly result in a lower daylight autonomy than for the façade with the light shelf.

A word of caution on using the IES LM-83-12 blind control criterion in the tropics, where the diffuse sky is a major source of glare. In the tropics, users will typically engage blinds both to shield against direct sunlight entry as well as from views to the glary bright white diffuse tropical sky. As such, the simulated daylight autonomy for automated blinds shown in the graphs is arguably unrealistically high for the tropics.

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